Aluminum-base alloy



Patented Mar. 24', 1931 UNITED STATES PATENT OFFICE THEODORE W. BOSSERT,OF NEW KENSINGTON, AND JOSEPH A. NOCK, JR., OF TAREN- TUM, PENNSYLVANIA,ASSIGNORS T ALUMINUM COMPANY OF AMERICA, OF PITTS- B'O'RGH,PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA ALUMINUM-BASE ALLOY NoDrawing.

The invention relates to aluminum base alloys, by which is meantthroughout this specification, and in the appended claims, alloyscontaining aluminum in amounts greater than about 90 to 95 per cent.

Phe adaptability of aluminum alloys to use in various shapes and formsis determined in part by two factors, the workability of the alloy andthe strength and stiffness of the J final product. One factor modifiesthe other, and often the production of a fabricated arti- ('le ofcertain strength and stiffness is precluded by the fact that an alloycapable of developing those certain properties is not capable of beingmechanically formed or worked into the desired shape. On the other hand,an alloy which will Withstand the working operation may not be capableof developing the required strength and stiffness in the finishedarticle.

An object of the invention is to provide an aluminum base alloy havingsuch a oombination of useful properties as will meet the demand for amaterial of moderate cost, good mechanical properties, superiorcorrosion resistance, and an unusual adaptability to the ordinarymethods of working, such as drawing, forging, swaging, extrusion, andthe like.

A further and important object of the invention is to provide analuminum base alloy from which an article of considerable strength andstiffness may be formed under severe metal-working conditions.

We have discovered that an aluminum base alloy containing manganese inamounts of from about 1 to 1.5 per cent, and magnesium in amounts offrom about 0.5 to 1.5 per cent, possesses the general combination ofdesirable properties above mentioned, and, in addition thereto, isinherently capable of fabrication, under given metal Working conditions,into an article of greater strength and hardness than is usuallyobtainable with any known aluminum alloy of similar workingcharacteristics.

The drawing and extruding characteristics of the new aluminum base alloycontaining magnesium and manganese are equal or su perior to prioralloys of similar characteris- Application filed June 5, 1930. SerialNo. 459,417.

tics, of which prior alloys an aluminum base manganese alloy containing1 to 1.5 per cent of manganese is an example, such alloy having hithertobeen considered to have excel lent adaptability to the types of workingconditions herein contemplated. Under given metal-working conditions,the strength and stiffness of a finished article made from our newaluminum-manganese-magnesium alloy is greater than the strength andstiffness of articles made from known alloys of similar workingcharacteristics, such as the aluminum base manganese alloy containing 1to 1.5 per cent of manganese.

A further important property of our new alloy rests in' its resistanceto static deformation under a constant and sustained load. Thisproperty, usually known as resistance to creep, is important wherever anarticle must support heavy loads over a Wide and comparativelyunsupported area, as when, for

instance, corrugated sheet metal is so used for roofing that 1t mustwithstand the deformation caused by sustained and heavy stresses such asthose produced by large amounts of snow. In this respect, ouraluminum-magnesium-manganese alloy is superior to an aluminum-manganesealloy of the composition above mentioned. For instance, an aluminumalloy containing about 1.25 per cent of manganese, and in the form of asheet strip 1 inch wide resting on supports 8 inches apart, wassubjected to a constant and sustained load by placing a weight at apoint midway between the supports, which load subjected the sheet to amaximum fibre stress of about 20,000 pounds per square inch. U11 derthese conditions, the deflection from the horizontal which initiallyresulted from the application of the weight was increased 0.026 of an.inch in 30 minutes. Under these exact conditions, an aluminum base alloyembodying our-invention, and containing 1.25 per cent of manganese and 1per cent of magnesium, exhibited an increase, from the deflection whichinitially resulted from the application of the load, of only 0.002 of aninch at the end of 30 minutes.

Within the limits of from about 1 to 1.5 per cent of manganese, theamount of that element may be varied without materially affecting thedesirable properties of our aluminum base alloy. So also, the magnesiumcontent may be varied between 0.5 and 1.5 per cent to produce alloys-ofthe nature contemplated by this invention. An aluminum base alloycontaining 1.25 per cent of magnesium and 1.25

. per cent of manganese has the desired properties, as do alloyscontaining 1.25 per cent of manganese and 1 per cent of magnesium, and1.5 per cent of manganese and 1.25 er cent of magnesium. We have found tat alloys containing as low as 0.5 per cent of magnesium together with 1to 1.5 per cent of manganese also serve the purposes and produce theeffects contemplated by our invention. However, the preferred alloyscontain between about 1 to 1.5 per cent ofeach of the elements magnesiumand manganese.

The mechanical properties of these new alloys vary according to therelative amounts of manganese and magnesium present, but the variationis not of great magnitude. For instance, the tensile strength vof alloysof the composition ranges above named does not, in the annealed or softcondition, deviate greatly from limits of about 22,000 to about 30,000

pounds per square inch. While the yield point of the same alloys isgenerally within a range of about 8,000 to about 10,000 pounds persquare inch, the percentage elongation in 2 inches varies'between about18 and 30 er cent. These properties, while not compara 1e with the prorties of what are generally designated as t e strong aluminum alloys,are very favorable when the fact is considered thataluminum base alloyscontaining manganese and magnesium in accordance with this inventionhave working characteristics which are better than those alloys ofequivalent or greater strength and hardness.

The alloys may be made from either commercial aluminum, which ma containfrom about 0.4 per cent or more 0 im urities, or from aluminum ofextremely high purity which may contain amounts as low as 0.02 per centof impurities, but in either case, the desirable properties of the alloyare retained. In alloys of this general type, it is well known to addamounts of either iron or silicon or both, which elements are commonimpurities in the commercial aluminum. We have found that the beneficialeffects obtained with loys embodying our invention are exceedinglyresistant to the action of corrosive agents. For example, we have foundthat when samples of these alloys are subjected to the action of saltsolutions, their resistance to corrosion is su erior to that of otheraluminum alloys of ii e strength and hardness, and is also,surprisingly, somewhat su rior to that of the ordinary commerciaaluminum.

According to the provisions of the patent statutes, we have ex lainedthe princi 1e of our invention, and ave given spec' c examples of itscharacteristics and properties. However, we desire to have it understoodthat, within the scope of the ap nded claims, the invention may bepracticeditherwise than as herein specifically described andexemplified.

We claim as our invention:

1. An aluminum base alloy containing from about 1 to about 1.5 per centof manganese and from about 0.5 to about 1.5 per cent of magnesium, thealuminum content being not less than about 95 per cent, and the alloybeing free from other alloying constituents except those present asimpurities.

2. An aluminum base alloy containing from about 1 to about 1.5 per centof manganese, and from about 1 to about 1.5 per cent of magnesium, thealuminum content being not less than about 95 r cent, and the alloybeing free from other a oying constituents except those present as imuritles.

In testimony w ereof, we hereunto sign our names.

THEODORE W. BOSSERT. JOSEPH A. NOCK, JR.

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